1. Field of the Invention
The present invention relates to a fault diagnosis apparatus for a crew protective apparatus which detects a collision of a car and operates, for example, an air bag, a seat belt pretensioner or the like.
2. Description of the Prior Art
FIG. 8 is a block diagram showing constitution of a collision detection apparatus of a car, such as disclosed in Japanese patent application laid-open No. 241467/1988. In FIG. 8, numeral 1 designates a DC power source such as a battery to be held on a car, numeral 2 designates a mechanical G switch in which contacts are closed by acceleration of a collision (hereinafter acceleration is referred to as "G"), numeral 3 designates a starting element called squib of a crew protecting apparatus, numeral 4 designates a transistor for switching currents flowing from the DC power source 1 to the starting element 3, numeral 5 designates a diagnosis circuit for carrying out fault diagnosis of the collision detection apparatus, numeral 6 designates a signal processing circuit which processes acceleration signals of the car at deceleration state and produces the amount of a collision and controls the transistor 4, numeral 7 designates an electronic G sensor which detects acceleration of the car at a deceleration state and outputs the detected acceleration to the signal processing circuit 6, and numeral 8 designates an alarm lamp which is lit when the diagnosis circuit detects a fault.
Next, operation will be described. The electronic G sensor 7 converts the amount of acceleration of the car at a deceleration state into electric signal and outputs the signal to the signal processing circuit 6. The signal processing circuit 6 performs signal processing such as integrating, amplifying, comparing the electric signal from the electronic G sensor 7 thereby a collision of the car is detected, and when the circuit 6 determines that an air bag must be unfolded, the transistor 4 is turned on. In this case, the mechanical G switch 2 is also turned on by the impact of a collision, and a current flows from the DC power source 1 through starting element 3 and the crew protecting apparatus is started.
On the other hand, the diagnosis circuit 5 forcedly operates the electronic G sensor 7 and the signal processing circuit 6 turns the transistor 4 on, and the terminal voltage of the transistor 4 is detected, thereby it is diagnosed whether or not the collision detection circuit constituted by the electronic G sensor 7, the signal processing circuit 6 and the transistor 4 operates normally, and if an abnormal state exists, the alarm lamp 8 is lit.
In this case, the diagnosis circuit 5 is supplied with car speed signal and parking brake signal being not shown, so that the fault diagnosis to turn the transistor 4 on is carried out only while the car is stopped.
Since the crew protecting apparatus is constituted as above described, in order to carry out the fault diagnosis of the collision detection circuit while the car is stopped, car speed signal, parking brake signal or the like must be taken and a harness or an interface circuit therefor must be provided in surplus.